A compact (1.8 by 3.0 by 3.8 cm) WR-10 waveguide amplifier module providing 310-mW power output, 20-dB gain, and 5 GHz of 1-dB bandwidth at a center frequency of 96 GHz is described. The module is comprised of 22 identical PHEMT chips, 4-way microstrip power combiners and dividers, and a 4-way waveguide power combiner

Byer, N.

Fischer, E.

Kane, B.

Weinreb, S.

Zimmerman, M.

Caltech Authors - Main

11-3 
W-BAND 0.3W PHEMT MMIC POWER AMPLIFIER MODULE 
S. Weinreb, E. Fischer, B. Kane, N. Byer, M. Zimmerman 
Martin Marietta Laboratories 
Baltimore, Maryland 
ABSTRACT 
A compact (1.8 by 3.0 by 3.8cm) WR-10 
waveguide amplifier module providing 310-mW 
power output, 20-dB gain, and 5 GHz of 1-dB 
bandwidth at a center frequency of 96 GHz is 
described. The module is comprised of 22 
identical pHEMT chips, 4-way microstrip power 
combiners and dividers, and a 4-way waveguide 
power combiner. 
INTRODUCTION 
A need exists for compact, W -band power 
amplifiers (PAs) with power in the 0.2- to 2-W 
range for use in small radars and communication 
systems. This power can be produced by 
combining a number of MMIC power amplifier 
chips. The efficiency of large millimeter-wave 
transistors (say >400-µm gate periphery at W-
band) and the efficiency of various types of 
power combiners limit both the power and 
overall efficiency at millimeter wave 
frequencies. This paper describes a 0.31-W 
amplifier that utilizes power combining of 16 
MMICs with a combination of microstrip and 
waveguide combiners to form a convenient in-
line WR-10 waveguide module. 
CONSTRUCTION 
A block diagram and a photograph of the 
module are shown in Figures 1 and 2. The 
MMIC power amplifier used throughout the 
module has been described in a previous 
paper[ll. In summary these MMICs provided 
>40 mW of power output from a 0.9- by 3.1- by 
0.1-mm GaAs chip utilizing four 0.1- by 
100-um pHEMT transistors with two transistors 
combined in the output stage. The PAs were 
25 
first tested on wafer for small signal phase 
match and power output with + 7 dBm of input 
power. The power output, efficiency, and gain 
of one of the best of these P As are shown in 
Figure 3. The phases of most of the tested PAs 
were within a ±20-degree window; the resulting 
5 degree rms phase error results in negligible 
power loss. 
Four three-stage MMIC power amplifiers 
were first combined on a carrier, which also 
contained a fifth identical MMIC used as a 
driver amplifier. The carrier included a 4-way 
microstrip GaAs power combiner and an 
identical chip used as a power divider. The 
four-way divider was comprised of three Lange 
couplers with four 300-µm fingers of 6-µm 
width and 6-µm spacing. These Lange couplers 
were somewhat overcoupled, which resulted in a 
loss from input port to each of the four-way 
outputs of 7.7, 9.3, 6.3, and 7.7 dB. To some 
extent this imbalance was compensated for by 
using the same chip rotated 180 degrees for both 
the power combiner and power divider; a 
channel that had more loss in the output 
combiner gets more drive power from the input 
power divider. 
The quad chip carriers were tested with 
wafer probes before integration into the module, 
and the power output versus power input for all 
four carriers is shown in Figure 4. The average 
output of 110 mW is consistent with an average 
chip power output of 41 mW and four-way 
microstrip power combiner loss of 1.7 dB. 
A compact four-way waveguide power 
combiner utilizing three rat-race ring hybrid 
junctions was constructed in a split-block, which 
forms the mounting base for the chip carriers. 
The ring hybrids were cut into each half of the 
split block and utilized 0.8 height waveguide 
95CH3577-7195/0000-0025$01.00 © 1995 IEEE IEEE 1995 Microwave and Millimeter-Wave Monolithic Circuits Symposium 
and H-plane right-angle bends to bring the 
inputs to an upper surf ace where the quad chip 
carriers were located. E-plane probe transitions 
from waveguide to grounded coplanar-
waveguide (CPW) were fabricated on small 
GaAs probe chips to allow three bond-wire 
connections (center conductor and two grounds) 
to CPW bond pads on the quad chip carriers. A 
backshort covered these transitions as can be 
seen in Figure 2. The termination of the fourth 
port of the ring hybrid was realized by means of 
200-ohm per-square tapered vane of metalized 
Mylar inserted within the split block along the 
center line of the waveguide. The insertion loss 
of a prototype ring hybrid was measured to be 
0.25 dB and the expected loss of the four-way 
waveguide combiner was 1.05 dB, allowing 
0.15 dB for waveguide loss and 0.35 dB loss for 
the waveguide probe to CPW transition. 
However, the measurements of 440 mW for the 
sum of the quad power outputs and 260 mW for 
the module waveguide output, both at 94 GHz, 
indicates a loss of 2.3 dB. It is believed that the 
additional 1.25 dB of loss arose from the gap in 
the backside ground plane in the CPW quad to 
CPW waveguide probe transition. Further 
evidence for this effect was the observation of 
small changes in output power when small 
metallic object were brought close to the 
transition region. The gap in the backside 
ground plane is being corrected on an improved 
module. 
26 
The module included a four-way microstrip 
input power divider realized by cascaded 
Wilkinson power dividers on 100-um-thick 
GaAs and two additional MMIC power 
amplifier chips at input to increase the module 
gain. Line lengths were carefully controlled to 
allow the input microstrip power divider to track 
the phase of the output waveguide combiner. An 
overall protective cover (not shown in the 
photograph) completed the module. 
PERFORMANCE 
The power output vs frequency for the 
module with +3 dBm of input power is shown in 
Figure 5, and the power output as a function of 
input power at a frequency of 96.4 GHz is 
shown in Figure 6. The power output at 1 dB 
gain compression is approximately +20 dBm. 
The module operates from a single +4.3 V 
supply and consumes 3.5 A for a total of 15 W 
of DC power. 
REFERENCE 
[l] S. W. Duncan, et al, "Compact High Gain W-Band and 
V-Band Pseudomorphic HEMT MMIC Power 
Amplifiers," Digest of Papers, IEEE 1994 Microwave and 
Millimeter-Wave Monolithic Circuits Symposium, San 
Diego, May 22-25, 1994, pp. 32-36. 
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Figure 1. Transmitter block diagram. 
4-WAY 
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Figure 2. Photograph of power amplifier module. 
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Figure 3. Characteristics of a single power-
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W-Band Power Module 
Power Output vs Frequency 
( Pin=3 mW, Vd=4V, Vg=+.2V, May 13, 1994) 
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Figure 5. Power output vs frequency for the 
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Measured Output Power vs Input Power 
Four Quad MMIC Power Amplifiers 
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Figure 4. Power ouptut vs power input for all 
4 MMIC carriers. 
W-Band MMIC Power Amplifier 
Output Power vs Input Power 
Module #1, Frequency 96.4 GHz, Vd=4V, ld=3.5A, Vg=+0.2V, 
( . 310 mV'f OUiputPowe~@25d8 Gain J 
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Figure 6. Power output vs power input for 
the complete module. 
5 


W-band 0.3W PHEMT MMIC power amplifier module

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W-band 0.3W PHEMT MMIC power amplifier module

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